<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="vue.js"></script>
</head>
<body>
    <div id="app">
        <transition name="fade" mode="in-out">
            <button v-bind:key="isoff" @click="isoff=!isoff">{{isoff?'off':'on'}}</button>
        </transition>
    </div>
    <script>
        var vm = new Vue({
            el:'#app',
            data:{
                isoff:false
            }
        })
    </script>
</body>
</html>